
/*
** Copyright (c) 2012 The Khronos Group Inc.
**
** Permission is hereby granted, free of charge, to any person obtaining a
** copy of this software and/or associated documentation files (the
** "Materials"), to deal in the Materials without restriction, including
** without limitation the rights to use, copy, modify, merge, publish,
** distribute, sublicense, and/or sell copies of the Materials, and to
** permit persons to whom the Materials are furnished to do so, subject to
** the following conditions:
**
** The above copyright notice and this permission notice shall be included
** in all copies or substantial portions of the Materials.
**
** THE MATERIALS ARE PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
** EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
** MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
** IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
** CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
** TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
** MATERIALS OR THE USE OR OTHER DEALINGS IN THE MATERIALS.
*/


#ifdef GL_ES
precision mediump float;
#endif
varying vec4 color;

void main (void)
{
    const float M_PI = 3.14159265358979323846;
    float c = 4.0 * 2.0 * (color.r - 0.5);
    float atan_c = 0.0;
    float scale = 1.0;
    float sign = 1.0;
    vec4 result;

    if(c < 0.0)
    {
        sign = -1.0;
        c *= -1.0;
    }

    if(c <= 1.0)
    {
        // Taylors series expansion for atan
        for(int i = 1; i < 12; i += 2)
        {
            atan_c += scale * pow(c, float(i)) / float(i);
            scale *= -1.0;
        }

        result = vec4(sign * atan_c / M_PI + 0.5, 0.0, 0.0, 1.0);
    }
    else
    {
        c = 1.0 / c;

        // Taylors series expansion for atan
        for(int i = 1; i < 12; i += 2)
        {
            atan_c += scale * pow(c, float(i)) / float(i);
            scale *= -1.0;
        }

        result = vec4(sign * (M_PI / 2.0 - atan_c) / M_PI + 0.5, 0.0, 0.0, 1.0);
    }

    gl_FragColor = result;
}
